I disabled "Memory Remap Feature" in my bios. It's some hack for Windows XP. Now I don't get that message, and EXA is decently fast with 6gb of ram.
This bug can be closed, it's not a driver bug, sorry...

I'm actually losing a lot. The bios is reporting back only 3 gigs of ram if i have that remap function disabled, when I boot up the kernel it says BIOS BUG! mtrr values don't cover physical memory, losing 3 gigs
I just posted on the asus forums, maybe they'll release a bios update. I'm done messing with this. 2 gigs is good enough for now.
Maybe some day x will use PAT, or asus will release a bios update, or some xorg bug will be found and repaired.

Re Dylan's message #8:
I have some concerns about that kernel patch. It isn't clear to me that the rounding of MTRR region sizes that it does is guaranteed to work. It actually changes how some memory addresses are typed.
The mtrr-uncover program leaves all addresses typed with the same type, even though this is accomplished via different MTRR values.
On the other hand, Ingo and Linus are rather knowledgeable.